The present invention relates to a method and apparatus for adjustably mounting optical elements. More particularly, the present invention relates to the testing of aspheric optical components by using interchangeable computer generated holograms (CGH) releasably coupled to an optical mount.
Laser interferometers provide the standard means for precision figure metrology of optical components and the transmission testing of optical assemblies. Accessory optics, such as Fizeau transmission spheres, produce spherical test light beams required by most testing configurations. Aspheric components, however, cannot be adequately tested using spherical light beams. One alternative is to use a refractive or reflective null compensator to generate an aspheric test light beam, but such compensators are expensive and time consuming to produce and certify. Another alternative is to use a Computer Generated Hologram (CGH).
CGH null compensators are more easily produced, certified and, consequently, less expensive and easier to use in testing aspheric components than the above methods. A CGH null compensator is a type of diffractive optic element consisting of a binary fringe pattern defined lithographically on a photomask or other planar substrate. The fringe pattern may be of chrome on glass or else etched into the substrate, the latter providing a higher diffraction efficiency. CGH null compensators may be designed for operation having either light transmission or light reflection. CGH null compensators, however, are difficult to align in standard interferometers and usually require a custom built interferometer, while still introducing difficult alignment issues.
There is a need for an apparatus and method for adequately testing aspheric optical components using a conventional interferometer and removing difficult alignment problems of CGH null compensators, thus conserving resources and simplifying testing procedures.